Heat-shield for gas-burning flare in oil production installations, particularly platforms at sea

ABSTRACT

A process to protect oil production installations from heat radiation given off by the flame of a gas-burning flare. In said process, a heat-shield is installed a short distance below the flare nozzle, to protect installations from at least part of the heat radiated by the flare flame.

This invention concerns a process to protect oil productioninstallations from heat radiation given off by the flame of agas-burning flare; it also concerns a heat-shield for a flare in such aninstallation particularly on a platform at sea.

Production of liquid hydrocarbons involves large quantities of gas,which must be removed or eliminated.

Flares also need to be provided on gas production fields, for safetyduring operations.

Various techniques have already been put forward and used to eliminatethis gas.

The gas is usually burned at the outlet of a flare located some distancefrom the actual installations, and connected to them by pipeline.

At sea, this arrangement obviously means that the flare outlet has to belocated far enough from the installation to ensure that normaloperations are not interfered with by the large amount of heat radiationthat always accompanies combustion of gas.

One suggestion has been to position the gas-burning flare actually onthe platform, but suspended beyond it. For structural and economicreasons, the distance between platform and burner nozzle is usuallyconfined to about fifty meters, so that the amounts of gas that can beeliminated are correspondingly restricted.

Surplus gas is sometimes simply released into the atmosphere through acold outlet; however, it is always subject to accidental ignition, sothat the platform still needs to be protected against the heat radiationthat would result.

The purpose of this invention is to reduce the effect of heat radiationgiven off by the flare flame, particularly on sensitive parts of theinstallation, while allowing the flare to be installed on the platformitself.

This invention concerns a process to protect oil productioninstallations from heat radiation given off by the flame of a gasburningflare, in which the gas is ejected at a high enough velocity to ensurethat a major portion of the flame beyond the flare nozzle remainsvertical, regardless of wind-speed, and in which at least part of theheat radiated directly towards the platform is shielded. The platform istherefore shielded from the direct radiation which the straight portionof the flame would otherwise give off in the direction of the platform.

In one embodiment of this process, radiation is blocked by installing aheat-shield a short distance below the flare nozzle.

In another embodiment of the process, the gas is ejected at a velocityof more than 0.2 Mach.

In general, the flare nozzle is specifically designed to ensure asufficiently high ejection velocity.

In preferred embodiments, the heat-shield consists of at least onecircular disc or conical structure on the same axis as the flare pipe.In another embodiment, this heat-shield consists of a number ofconcentric flat rings or truncatedconical structures.

This invention also concerns a heat-shield for application of this newprocess, comprising an approximately horizontal screen with a reflectingtop surface, surrounding a tall vertical flare pipe, the upper part ofwhich forms the flare nozzle.

In one embodiment, the flare pipe is supported along part of its heightby the drilling rig, which is surmounted by a structure forming asupport for a framework to support the heat-shield.

In another embodiment, the heat-shield is constructed fromstainless-steel plating, polished on top and supported on the frameworkby means of banded elastomer blocks designed to permit the plating toexpand freely and to insulate it from the framework and supportingstructure.

Consequently, as will be described in detail below, the heat-shieldintercepts most of the heat radiation given off by the burning gas,which would otherwise raise the temperature of the surface of theinstallation at the base of the flare, preventing normal operations fromtaking place.

It will be easier to understand the features of the invention from thefollowing description, given solely as an example, with reference to theaccompanying drawings:

FIG. 1 is a diagrammatical view in elevation of a platform equipped witha gas-burning flare fitted with this new heat-shield.

FIG. 2 is a cross-section of a heat-shield in the form of a singlecircular ring.

FIG. 3 is a cross-section of a heat-shield in the form of a number offlat concentric circular rings.

FIG. 4 is a cross-section of a heat-shield in the form of a number oftruncated-conical concentric circular rings.

FIG. 5 is a guidance chart, showing some levels of radiations given offby the flare flame, level with the platform flooring, in relation to thedistance from the base of the flare, for some local wind velocities.

FIG. 1 provides a diagrammatical view of a drilling and processinginstallation, comprising a platform 10, supported by a number of columns12 connected together for strength and each resting on a caisson 13.

The platform carries a processing plant 14 and various installations 15and 16, as well as a drilling rig 20, constructed in the usual way fromsteel sections, in the general overall shape of truncated pyramid veryelongated in height. This rig normally rises about 50 m above the floorof the platform, which may cover an area within a 50 m radius.

For this invention, the drilling and treatment plant is equipped with avertical flare pipe 21, running from the processing installations alongthe drilling rig, against which it is held, and ending in a nozzle 22which is 60 m above the platform floor.

A structure 25, consisting of tubular and angular sections, attached tothe upper end 24 of the rig, supports the flare nozzle.

This structure 25 also supports a heat-shield 27, consisting of anapproximately horizontal screen surrounding the pipe 21 and located ashort distance e below the flare nozzle 22; e is approximately 1.5 m.

Gas resulting from production processes is dispatched along the pipe 21and ignited at the nozzle, producing a flame 30, approximately 55 m highin this example.

Energy given off towards the platform by this flame 30 is partlyintercepted by the heat-shield, which may be in the form of a circulardisc coaxial to the flare pipe, approximately 15 m in diameter. Toensure greater effectiveness, the top surface of the heat-shield shouldbe reflecting.

To make it easier for the air below the heat-shield to reach the flameand to prevent the disturbances that would otherwise be caused byair-streams skirting round the disc 27, the heat-shield is designed inthe form of an annular element, as shown in elevation e.g. in FIG. 3.The screen 27 contains a circular opening 27', the diameter of which mayrange from 2 to 6 times the diameter of the flare pipe 21.

FIGS. 3 and 4 each show a cross-section of a heat-shield consisting of anumber of concentric rings 27a, 27b and 27c. Moving away from the flarepipe, the outside diameter of each of these rings is at least equal tothe inside diameter of the following ring, and the edges of adjacentrings are kept apart.

In FIG. 3, the shield consists of flat rings 27a', 27b', 27c', the innerand outer edges of which are bent in a substantially S-shaped manner, sothat the edges of adjacent rings are not in contact.

In FIG. 4, the shield consists of truncated conical rings, and the edgesof adjacent rings are kept apart by positioning the ring surfaces atdifferent respective levels along the centerline of the flare pipe.

The embodiments shown in FIGS. 3 or 4 allow air to pass through theshield in an upward direction, which both cools the shield and suppliesthe base of the flame with air for combustion.

In one embodiment, the heat-shield 27 consists of stainless-steel sheetelements with a polished upper surface, supported on the framework 25 bymeans of ferruled or iron banded elastomer blocks which permit the sheetelements to expand freely, and insulate it from the framework.

If no wind is blowing over the platform, the flame 30 remains vertical,as shown in FIG. 1. In this case, the central part of the platform isprotected against any heat radiation given off by the flame, and it isonly at a certain distance D from the center of the platform that thefloor is subject to radiation, the approximate value of which is shownin the chart in FIG. 5 by the continuous line, in relation to D,expressed in BTU/Sqf/hr and corresponding to a gas flow-rate of1.8375×10⁶ SCF/hr (i.e. 1.15×10 Nm³ /day), the flare nozzle being sodesigned that the gas is ejected at a velocity of 0.3 Mach.

If a wind of 57 m/sec (i.e. approximately 200 km/hr) is blowing, the topof the flame 30 bends under its force, taking up position 30' at anangle of approximately 33° to the vertical, while the lower part of theflame remains almost vertical. The screen then no longer intercepts allof the heat radiation given off by the flame in the direction of thecentral part of the platform. If the wind velocity is 45 m/sec (162km/hr), the flame 30 bends at an angle of 27° to the vertical.

The broken line on the chart in FIG. 5 shows distribution of heatradiation reaching the platform in the case of a wind velocity of 57m/sec.

Although radiation in this case is higher, it is still below an upperlimit S below which exposed parts of the platform may be used normally.Depending on the function of the exposed area, this limit S ranges from440 to 2,000 BTU/H/Sqf (i.e. from 1195.4 to 5424.6 kcal/H/m²).

For information, it should be remembered that the calorific effect isproportional to the inverse square of the distance between the point ofemission in the flame and the point on the platform receiving radiation.

In fact, it is the parts of the flame closest to the flare nozzle thathave the greatest effect, and this is precisely where the heat-shield ismost effective.

The closer the shield is to the flare nozzle, the more radiation it willblock; however, for technological reasons, involving expansion andstrength of materials, experience shows that a distance of 1 to 3meters, and preferably 1.5 meters, is both acceptable and effective.

Similarly, the diameter of the shield, which is approximately 15 m inthe example described here, may vary depending on the length of flameand composition of gas.

For all these reasons, values and figures quoted above are given purelyfor guidance, and may be altered depending on specific operatingvariables.

The heat-shield may consist of a single sheet or of component partsassembled by any appropriate method.

Naturally, this invention is in no way confined to the embodimentsdescribed and illustrated here: many variations are possible for someoneskilled in the art, depending on what applications are involved andwithout any departure from the spirit of the invention.

What is claimed is:
 1. A process of protecting at least a selectedportion of the area of an oil production installation from the heatradiation emitted by the generally upwardly extending flame produced atthe outlet of the nozzle of a gas burning flare mounted on the top endof a generally vertical flare pipe extending from a platform supportingsaid installation, said selected area portion being defined about thegeometrical axis of said flare pipe, comprising the steps of:ejectingsaid gas to be burned through said nozzle at a flow velocity higher thanMach 0.2 and shielding said selected area portion from said heatradiation by providing, at a distance of 1 to 3 meters below said nozzleoutlet, substantially horizontal annular heat shielding means made ofstainless steel sheet and means having an outer periphery and an innerperiphery which delimits a central circular aperture the diameter ofwhich equals about2 to 6 times the diameter of said flare pipe, saidinner periphery concentrically surrounding said flare pipe.
 2. Theprocess of claim 1, wherein said heat shielding means comprises a singleannular heat shielding element.
 3. The process of claim 1, wherein saidheat shielding means comprises a plurality of concentric annular heatshielding elements, and an annular cooling air passage is providedbetween any two adjacent ones of said concentric elements.
 4. Theprocess of claim 1, wherein said heat shielding means comprises aplurality of concentric frusto-conical annular heat shielding elementseach having an outside diameter at least equal to the inside diameter ofan adjacent shielding element, said shielding element being disposed insuch a manner that an annular cooling air passage is defined between anytwo adjacent shielding elements.
 5. The process of claim 1, wherein saidheat shielding means comprises a plurality of concentric annular heatshielding elements each having a substantially S-shaped profile and anoutside diameter at least equal to the outside diameter of an adjacentshielding element, said shielding elements being disposed in such amanner that an annular cooling air passage is defined between any twoadjacent shielding elements.